Mpox breakthrough infections: concerns and actions

Abstract

There have been more than 88000 cases of mpox (formerly known as monkeypox) disease, caused by monkeypox virus (MPXV), since May, 2022. In 2019, the US Food and Drug Administration (FDA) approved the modified vaccinia Ankara–Bavaria Nordic (MVA–BN) vaccine as a two subcutaneous dose regimen to prevent Comment www.thelancet.com/infection Vol 23 November 2023 1217 Flickr - Tony Oliveira/ Agência Brasília smallpox and mpox infection.1 During the 2022–23 outbreak, the pooled estimated vaccine effectiveness in preventing mpox infection was 89%.2 Despite that good effectiveness, breakthrough infections can occur, due to various factors, including the host immune response variations or exposure to high viral loads. A recent study in the UK reported that eight of 363 mpox cases assessed were likely to have occurred at least 14 days after receiving a single-dose MVA–BN vaccine.3 Notably, 32 cases occurred within two weeks of vaccination. In another study,4 77% of post-vaccination cases occurred within two weeks...